JSFiddle - React, Tailwind, and code Playground

HTML

Move over should show an animated yellow box<br>
<div class="outer">
    <div class="inner"></div>
</div>
<br>
1. outer div changed to position fixed<br>
2. yellow box should fade in<br>

CSS

.outer {
    position: relative;
    padding: 10px;
    background-color: green;
}

.inner {
    opacity: 0;
    background-color: yellow;
    width: 100px;
    height: 100px;
}

.outer:hover {
    position: fixed;
    top: 0;
    width: 100%;
}

.outer:hover .inner {
    opacity: 1;
    transition: opacity 1s;
}